MODULATOR AND DEMODULATOR OF 107Gbd BPSK, QPSK &
16QAM
C.Vasantha Kumar1, P.Sangeetha2
1Assistant
Professor, Department of Electronics and Communication
Engineering, Maharaja Institute of Technology, Coimbatore Tamilnadu, India,
2AssistantProfessor, Department of Electronics and Communication Engineering,
Kongu Engineering College, Tamilnadu, India
ABSTRACT
This paper presents 107-GBd coherent optical system for the generation and reception of M-ary Phase-Shift
Keyed (PSK) and Quadrature-Amplitude Modulated (QAM) signals, including Nyquist pulse shaping. It is based
on phase-stable Optical Time-Division Multiplexing (OTDM) of two tributaries, which are modulated at half the
target symbol rate, optical Nyquist filtering, and a broadband digital coherent receiver. QAM is very widely used in
cable TV, Wi-Fi wireless local-area networks (LANs), satellites, and cellular telephone systems to produce
maximum data rate in limited bandwidths. The most common forms of modulation are BPSK, QPSK, and several
levels of QAM. BPSK, QPSK, 16QAM, and 64QAM are defined with 802.11n.These basic modulation forms are
still used today with digital signals for spectral efficiency. It has Nyquist pulse shaping that ensures narrowest
possible signal spectrum without creating inter-symbol interference and therefore increases the spectral efficiency.
It has reduced the hardware speed requirements that enables lower penalties with respect to theory of all ETDM
experiments so far. This model is highly efficient and robust for demonstration of modulator for SDR and other
wireless standards.
Keywords:
Coherent
detection,
Time-Division Multiplexing,
Quadrature-Amplitude
Modulation
1.1 Introduction
The main goal of modulation today is to
squeeze as much data into the least amount of
spectrum possible. Multiple techniques have emerged
to achieve and improve spectral efficiency. The
existing system with BPSK modulation technique
gives good spectral efficiency, since each carrier
phase represents two bits of data. But it transmits
fewer bits per symbol, with reduced baud. Proposed
system with 16QAM, QPSK, have more symbols
transmitted and bit error rate is reduced using optical
Nyquist pulse shaping criterion. It implies lower
penalties with respect to theory compared to allETDM experiments presented so far. This project
helps to compare a BPSK/QPSK/QAM system to
find most efficient modulation techniques.
1.2 Related Work
G. Raybon in his work titled “All-ETDM
107-Gbaud PDM-16QAM (856-Gb/s) transmitter
and coherent receiver,” proposed the generation of
all- electronically multiplexed 107-Gbaud PDM16QAM and its coherent detection using 72-GHz
balanced photo detectors and a 63-GHz real-time
oscilloscope. Symbol rates up to 107 Gb/s using
electronically multiplexed transmitters and receivers
have been previously demonstrated in direct
detection experiments using binary modulation
formats1,2, and in coherent detection experiments
using quadrature phase shift keying3 (QPSK). In
order to achieve higher per-carrier line rates,
quadrature amplitude modulation (QAM) has
recently been demonstrated up to 80 Gbaud,
providing 640 Gb/s on a single carrier4 and 1.28 Tb/s
in a dual-carrier system5. Here, generation and
detection of the highest dual-polarization singlecarrier line rate of 856 Gb/s is demonstrated using
all-electronic multiplexing (ETDM) to 107- Gbaud
16QAM.
1.3 Paper overview
BER comparison of Optical Nyquist QPSK,
BPSK, and 16QAM is simulated to find out most
efficient modulation technique based on phase-stable
Optical Time-Division Multiplexing (OTDM) of two
tributaries that modulated at half the target symbol
rate, optical Nyquist filtering, and a broadband digital
coherent receiver. Greater the number of small
phase shifts the more difficult the signal to
demodulate in the presence of noise so optical
nyquist criterion used to reduce inter symbol
interference.
1.4 Proposed Model:
sample N times, where N is the Pulse length
parameter. After replicating input samples, the
block can also normalize the output signal and/or
apply a linear amplitude gain. If the pulse delay
parameter is nonzero, then the block outputs that
before starting to replicate any of the input value.
1.4.6 Up Converter and Down Converter
Analog Devices digital up/down converters
serve as the frequency translator and digital filter
between data converters and DSP block. These
innovative products enable highly programmable and
configurable receive and transmit signal chains,
allowing multi-channel, multi- carrier radio platforms
in 3G wireless base stations. They also meet the
digital data conversion requirements for many other
communications application.
Fig 1: Block diagram of 107
BPSK/QPSK/QAM
Modulator
Demodulator
Gbd
and
1.4.1 Error Rate
This block represents calculation of error rate
performances of input transmitted modulated signals
and demodulated signals.
1.4.2 Random Integer Generator
This block allows generating random
integers. The randomness comes from atmospheric
noise, which is used for many purposes. It is better
than the pseudo-random number algorithms which
are typically used in computer programs.
1.4.3 General BPSK Modulator
This block acts as a modulator for input
signal transmission operation. The given input
signal is to be modulated for input transmission
operations.
1.4.4 Binary Phase Shift Keying (BPSK)
A very popular digital modulation scheme, binary
phase shift keying (BPSK), shifts the carrier sine
wave 180° for each change in binary state .BPSK is
coherent as the phase transitions occur at the zero
crossing points. The proper demodulation of BPSK
requires the signal to be compared to a sine carrier
of the same phase. This involves carrier recovery
and other complex circuitry.
1.4.5 Rectangular Filter
The Ideal Rectangular Pulse Filter block
up samples and shapes the input signal using
rectangular pulses. The block replicates each input
1.4.7 Integrator
An integrator is a device to perform the
mathematical operation known as integration, a
fundamental operation in calculus. Here, this
integrator block is to be used for the demodulation
process. The multiplied signals are integrated with
modulated carrier signals for demodulation.
1.4.8 General BPSK Demodulator
Here, this block acts as a demodulator for
modulated signal re-transmission operation. The
modulated signals are again demodulated for getting
an original message signal for the re-transmission
operation.
1.4.9 Nyquist Filter
A Nyquist filter is an electronic filter used in
TV receivers to equalize the video characteristics. It
reduces inter symbol interference. Nyquist bandwidth
is the minimum transmission bandwidth for zero
intersymbol interference. In order to equalize the low
frequency and high frequency components of the VF
signal, a filter named a Nyquist filter is used in
receivers. This filter, which is used before
demodulation, is actually a low-pass filter with 6 dB
suppression at the intermediate frequency (IF) carrier.
Thus the level of double sideband portion of the VF
signal is suppressed and the original band
characteristic is reconstructed at the output of the
demodulator.
1.4.10 Coherent Technology
This Technology includes dispersion
compensation modules. Intraditional wavelength
division multiplexing (WDM) networks, DCMs or
tunable dispersion compensation modules (TDCMs)
are placed at amplification sites along the line to
compensate for chromatic dispersion. These modules
introduce loss (meaning additional amplification is
required) and non-linear distortions. Amplification
and non-linear effects increase the addition of optical
noise on the line, thereby reducing transmission
reach. In contrast, electro-optics with coherent
technology enables electronic-based dispersion
compensation at the receiver end. This removes the
need for DCMs and improves total transmission
reach.
1.4.11 Quadrature Amplitude Modulation (QAM)
The creation of symbols that are some
combination of amplitude and phase can carry more
bits per symbol. This method is called quadrature
amplitude modulation (QAM). 8QAM uses four
carrier phases plus two amplitude levels to transmit 3
bits per symbol. Other popular variations are
16QAM, 64QAM, and 256QAM, which transmit 4,
6, and 8 bits per symbol respectively. Here, there are
three amplitude and 12 phase shifts. While QAM is
enormously efficient, it is more difficult to
demodulate in the presence of noise, which is mostly
random amplitude variations. Linear power
amplification is also required. QAM is very widely
used in cable TV, Wi-Fi wireless Local-Area
Networks(LANs), satellites, and cellular telephone
systems to produce maximum data rate in limited
bandwidths.
BER comparison of Optical Nyquist QPSK,
BPSK, and 16QAM is simulated to find out most
efficient modulation technique. The system is
analyzed in back-to- back experiment with Binary
PSK (BPSK) modulation, Quadrature-PSK (QPSK)
modulation, as well as with 16- ary QAM.BER
performance of all the modulation techniques namely
BPSK, QPSK, 8PSK, 16PSK, 16QAM is analyzed
without using any block codes. The transmitter is
based on independent electro-optical modulation of
two time- division multiplex tributaries and
subsequent optical interleaving after modulation.
Greater the number of small phase shifts the more
difficult the signal to demodulate in the presence of
noise. So Optical Nyquist criterion is used to reduce
inter symbol interference and to increase spectral
efficiency. The major advantage is that BER
performance achieved is in good level. The present
system describes a less noise, and good spectral
efficiency with BPSK modulation.
Fig 2: Constellation Diagram
Modulation
Technique
BPSK
QPSK
16 QAM
BER
PSNR
0.9032
0.8782
0.871
-13.8
-15.6
-6.02
Table 1: Performance Comparison
The existing system make use of BPSK
modulation technique for which BER measured up
to 60Gb/s using BER tester. BPSK Modulation is
applied to double the data rate at terahertz
frequencies conducted at 60 Gb/s and 50Gb/s
operation with a low bit error rate. BPSK have less
phase shift and more bits cannot be transmitted per
symbol, result in reduced data rates. It mainly
consists of: Input sequence, General modulation,
Product modulation, General demodulation, Bit
performance measurement. This system makes use of
only QPSK modulation technique. If Optical Nyquist
pulse shaping is not performed, it will result in inter
symbol interference. The data rate is reduced because
of fewer bits per symbol transferred. Here BER Vs
PAPR reduction done, BER is Bit Error Rate, PAPR
is Peak Average Power Ratio. Reductant level is up
to 10 and above range.
1.5 Results and Discussions
The realized implementation penalties
compared to theory at the BER of 1 × 10−3 are 0.5
dB, 1.5 dB and 6 dB for BPSK, QPSK and 16QAM,
respectively. For a realization at such high symbol
rates of 107-GBd, the penalties can be considered as
small, even for the 16QAM system. We attribute the
higher penalties in the case of 16QAM mainly to
imperfections in the generated signal at the base rate
of 53.5-GBd. The aggregated signals were received
error-free, assuming conventional forward error
correction with 7% overhead. This model is highly
efficient and robust for the demonstration of
modulator for SDR and other Wireless standards. The
major advantage is that as BER performance is at
good level, it reduces hardware speed requirements
that enable lower penalties with respect to theory
compared to all-ETDM experiments. It has Nyquist
pulse shaping that ensures narrowest possible signal
spectrum without creating inter-symbol interference
and therefore increases the spectral efficiency. For a
realization at such high symbol rates of 107- GBd,
the penalties can be considered as small, even for the
16QAM system. We attribute the higher penalties in
the case of 16QAM mainly to imperfections in the
generated signal at the base rate of 53.5-GBd. The
aggregated signals were received error-free,
assuming conventional forward error correction with
7% overhead.
1.6 Conclusion
The generation and broadband coherent
reception of optical 107-GBd Nyquist-shaped signals
is modulated with different modulation formats,
namely BPSK, QPSK and 16QAM. Two-fold phasestable optical multiplexing was used in order to
ensure high-quality IQ-modulation. Nyquist pulseshaping was applied in the optical domain by use of a
programmable
optical
filter.
The
realized
implementation penalties compared to theory at the
BER of 1 × 10−3 are 0.5 dB, 1.5 dB and 6 dB for
BPSK, QPSK and 16QAM, respectively.
For a realization at such high symbol rates
of 107- GBd, the penalties can be considered as
small, even for the 16QAM system. We attribute the
higher penalties in the case of 16QAM mainly to
imperfections in the generated signal at the base rate
of 53.5-GBd. The aggregated signals were received
error-free, assuming conventional forward error
correction with 7% overhead.
Future work involves the achievement of
total net data rate to about 400-Gb/s for 107- GBd
single-polarization 16QAM. A straight forward
doubling of the net rate to 800-Gb/s is also possible
by applying PDM. Generation and coherent reception
of optical Nyquist 16QAM technique is to be applied
in antennas to increase data rate and to reduce BER.
1.7 References
[1] Ho-Jin Song, Katsuhiro Ajito, and Jae- Young
Kim(2014)
,“50-Gb/s
Direct
Conversion
QModulator
and Demodulator MMICs for
Terahertz Communications at 300 GHz ,” IEEE
Trans. Microwave theory & technique Conf .vol
62.no. 3, pp. 127-128.
2. Fischer. J, (2011)) “8 × 448-Gb/s WDM
transmission of 56-GBd PDM 16-QAM OTDM
signals over 250-km ultra large effective area fiber,”
IEEE Photon.Technol. Lett.vol. 23, no. 4, pp. 239–
241.
3.Fontaine N. K. ,(2012) “228-GHz coherent
receiver using digital optical bandwidth interleaving
and reception of 214-GBd(856-Gb/s) PDM-QPSK,”
IEEE Trans.Commun Syst., vol. 21, no. 11, pp. 1600–
1611.
4. Huang Y.K,(2010) “10 × 456-Gb/s DP-16QAM
transmission over 8 × 100 km of ULAF using
coherent detection with a30-GHz analog to-digital
converter,” IEEE Trans. Opto-Electron. Commun
.,vol. 4, no. 3, pp. 285–295.